The operation of vehicles by persons under the influence of alcohol is a major safety problem in the United States and many other countries. Despite growing public awareness and government concern, statistics continue to show that a high percentage of automobile accidents causing serious injury or death involve drivers who have been drinking alcoholic beverages in excess. Injuries in the workplace are also often found to be related to the operation of heavy equipment or other machinery by persons impaired by the effects of alcohol.
To address this problem, various attempts have been made to develop devices intended to prevent automobiles and the like from being operated by inebriated individuals. Such devices, which are commonly referred to as "sobriety interlocks" are often based on the well known principle that the gas present in the alveoli of the lungs has an alcohol content directly proportional to that of the bloodstream. Blood alcohol content (BAC) thus can be accurately determined by breath testing. A sobriety interlock is connected to the vehicle and normally operates to prevent the vehicle from being started unless one or more prerequisite conditions imposed by the interlock are satisfied. Foremost among such conditions is that any alcohol detected be present in a sufficiently low concentration although, the interlock may normally require a number of further conditions to be met before starting of the vehicle is enabled.
For example, it is generally acknowledged that to accurately determine BAC from a breath sample, an interlock must be designed to require delivery of a "deep lung" breath sample. As used herein, that term refers to a breath sample consisting of a proportion of alveolar gas sufficient to permit an accurate determination of blood alcohol concentration. Since breath expired from upper portions of the respiratory tract does not necessarily have an alcohol level proportional to that of the bloodstream, a deep lung sample is essential if an interlock is not to be defeated by shallow exhalations of a series of short puffs of breath expelled from upper portions of the respiratory tract.
This problem is addressed effectively in U S. Pat. Nos. 4,093,945 and 3,764,270 issued to Collier et al. The Collier et al. patents disclose means, such as a pressure switch and timer system, to ensure delivery of an essentially continuous and uninterrupted flow of breath sufficient to yield a deep lung sample. The sampling interval determined by the timer and the flow rate (as measured by the pressure sensor or other flow sensing means) are selected together to ensure a deep lung sample will be given. Unless breath is delivered at least a minimum predetermined flow rate without interruption for the entire sampling interval, a required condition is not deemed satisfied and the vehicle cannot be started.
Unlike breath analyzer tests which are usually administered under the supervision of police or other trained persons, sobriety interlocks are routinely used outside the presence of persons other than the vehicle operator/test subject whose use of the interlock may be less than completely voluntary. One example of such a situation is where an employer seeks liability protection by installing interlocks on vehicles operated by employees. A higher degree of compulsion may be involved in some cases of court-supervised rehabilitation of offenders found to have been driving while under the influence of alcohol (DUI). As a mandatory condition for permitting a DUI offender to drive in order to maintain employment and/or obtain counselling, some courts may require a sobriety interlock to be installed in the offender's car. In such cases there is an increased likelihood that attempts to defeat the interlock will be made. Accordingly, the prior art has proposed various self-supervisory techniques directed toward avoiding circumvention of interlocks by various forms of subterfuge. While these techniques vary as widely as the forms of deception they seek to prevent, they share a common characteristic in that they require one or more additional conditions, usually unrelated to alcohol to be satisfied as prerequisites to starting the vehicle.
For example, techniques to discriminate between a contemporaneous breath sample and bogus gasses such air from a bicycle pump, filling station air hose or breath from a previously inflated balloon are discussed in U.S. Pat. Nos. 4,592,443; 3,831,707; and 3,824,537. Each of these patents proposes requiring one or more additional conditions be satisfied before permitting the vehicle to start. U.S. Pat. No. 4,592,443 requires the temperature of the gas delivered for a test to fall within a range expected for breath. Breath being moist, U.S. Pat. No. 3,831,707 requires the gas to contain appropriate humidity to avoid circumventing an interlock with a bogus gas that is drier than breath. U.S. Pat. No. 3,824,537 teaches requiring the operator to place one hand on a button which must be activated during a test period while the other hand is used to hold a breath sampling tube located some distance away from the button. Since both hands of the operator are placed apart, deceptive manipulation of a bellows or the like is discouraged. While all of these techniques have some merit, they are of little overall benefit if a sobriety interlock can be circumvented regardless of them by the simple artifice of enlisting the aid of a sober accomplice to take the test. This vexing problem is dealt with in U.S. Pat. No. 4,738,333 to Collier et al.
The technique proposed in the above '333 patent is to require the operator/test subject to identify himself or herself by correctly performing what is termed an "identity-confirming act" which the interlock is capable of recognizing. Unless this act is correctly performed within a limited number of attempts, the interlock will not permit the vehicle to be started regardless of the result of any alcohol breath test. Unlike a personal identification number (PIN) code which can be readily entered by another person who is merely given knowledge of the code, correct performance of the identity-confirming act requires a degree of skill which cannot ordinarily be acquired by most persons without attempting the act at least some minimum number of times. The limited number of attempts the interlock allows the act to be tried is selected to be lower than the minimum number of attempts ordinarily required to learn the act. In this way, the interlock can effectively discriminate between a trained designated person and a previously unskilled accomplice.
Notwithstanding the safeguards which have been developed in the prior art, it still cannot be guaranteed that sobriety interlocks are incapable of being bypassed. As used herein and in the claims, the term "bypass event" refers to an event whereupon the vehicle (or other machine) to which a sobriety interlock is connected is started without satisfying one or more of the conditions normally imposed by the interlock as prerequisites to permitting the vehicle to start. The realization that it is possible to bypass a sobriety interlock raises a crucial question. To wit, if at least some persons who are required to use a sobriety interlock discover how to start the interlocked vehicle without using the interlock to provide proper clearance for starting, how then can the interlock continue to remain an effective deterrent of drunken driving? The prior art has failed to deal effectively with this problem.